Natural plant-based phenolic compounds, such as flavonoids, have received much attention for their potent antioxidant properties. Phenolic compounds are present in many plant sources, such as fruits, vegetables and many herbal or aromatic plants. Given their potent anti-oxidant activities, plant phenolics have been under investigation as health-promoting substances for over 20 years.
Apples are a good dietary source of phenolic compounds. Apple peel has 3- to 6-fold higher flavonoid content than apple flesh and has unique flavonoids, such as quercetin glycosides, not found in the flesh (Wolfe, Wu & Liu, 2003; Wolfe & Liu, 2003).
Apple peel extracts have been shown to possess powerful free radical scavenging activity (Kondo et al., 2002). Various apple peel extracts and methods of making them are described, for example, in US 2005/0147723 A1, US 2006/0172012 A1, U.S. Pat. No. 6,440,410 B1, EP 0 659 347 A1, and Kim et al., 2005. PCT application WO 2009/0767776 A1 to Rupasinghe et al. discloses a crude extract derived from apple peel and its use in preventing oxidation of polyunsaturated fatty acids or lipids in food products.
Oxidative stress induced by reactive oxygen species is linked to a number of human conditions and diseases. Plant-derived antioxidants may therefore provide dietary modulators useful in preventing or treating a number of such diseases, including certain neurodegenerative diseases (Kaur and Kapoor, 2001; Heo et al. 2004). A ubiquitous flavonoid, quercetin 3-O-glucoside (Q3G), was recently suggested to have neuroprotective effects in vitro (Soundararajan et al., 2008). Direct treatment of neuronal cells in vivo is not a likely therapeutic approach however, and there is no indication that apple-derived extracts would have any beneficial effect in vivo.
The costs associated with neurodegenerative disorders are in excess of $20 billion annually in North America. Currently, there are no registered natural products with health claims for protecting against these neurodegenerative disorders. As our overall population ages, there is increased desire to maintain health as well as to use alternative medications derived from natural or biological sources. There is a need for discovery and development of safe and effective natural products to treat, prevent or reduce the risk of oxidative stress-mediated conditions and diseases, including neurodegenerative disorders.
Apple peels are a waste product of the apple processing industry in many countries and therefore represent and attractive resource for value-added health-promoting products. While crude extracts have been prepared, there is a need for more refined compositions having potent antioxidant properties. Extraction of phenolic compounds from plant sources presents challenges, since the phenolic compounds are easily oxidized and degrade under harsh extraction conditions.